passing an dynamic array as copy to recursive function c++ - c++

Question

I am writing code for a backtracking approach to a Traveling Salesman type of problem. So at each point i will recurse for rest of the un-visited points.
I could not use any library/functions other than cout, cin, new and delete (so no vector). So for the problem i want to keep a track of what all points i have visited till now. I am using a dynamic boolean array for this. So i want to pass the dynamic array to a function as value to keep track of this.
This is what i have tried till now.
I tried to wrap the array in a struct, but the memory dealocation (delete) is giving error (Segmentation fault)
typedef struct Barray{
bool* a;
int size;
Barray(int size) { a = new bool[size]; this->size = size; }
Barray(const Barray& in) {
if(a) delete[] a; // error
a = new bool[in.size];
this->size = in.size;
for (int i = 0; i < in.size; i++)
a[i] = in.a[i];
}
~Barray() { delete[] a; } // error
}barray;
This is my recursive function call
void find_mindist(barray visited, int dist_now, int cur_p) {
if (base condition)
{return ;}
for (int i = 0; i < n; i++) {
if (visited.a[i]) continue;
barray tdist = visited;
tdist.a[i] = true;
int ndist = dist_now + dist(points[cur_p], points[i]);
find_mindist(tdist, ndist, i);
}
return ;
}
So my questions are -
how can i pass a dynamic array to a function as value?
Why is the delete above giving error?

Answer 1

First of all, the recommended approach for a local visited information is not the endless copying of the whole visited collection, but a mark->recurse->unmark approach. So whatever you do, please keep a single boolean array for the visited information and update its content to your needs.
The other problems occur because you try to delete an uninitialized pointer in the copy constructor. Also, the assignment operator should be overloaded as well to avoid unpleasent surprises. But non of this really matters if you don't copy your visited information anymore.

Answer 2

The problem this is a copy constructor. As such, on entry, a is uninitialized (so contains garbage), so the delete is invalid.
Barray(const Barray& in) {
if(a) delete[] a; // error
a = new bool[in.size];
this->size = in.size;
for (int i = 0; i < in.size; i++)
a[i] = in.a[i];
}
Just remove the delete line. Also, prefer to initialize members, rather
than assign them, so:
Barray(const Barray& in)
: a(new bool[in.size])
, size(in.size) {
for (int i = 0; i < in.size; i++)
a[i] = in.a[i];
}
Also, remember the Rule of Three. You need an copy assignment operator. The simplest is:
Barry& operator=(const Barray& in) = delete;
which just forces a compilation error if you try to use it! Better is:
Barry& operator=(const Barray in) { // **NOTE** pass by value!
std::swap(this.a, in.a);
std::swap(this.size, in.size);
}
This version provides the strong exception guarantee. You aren't allowed to use std::swap, so you'll either have to write your own, or write it out by hand (you choose).
Finally, if you ever find yourself returning a Barray, you should write a move constructor:
Barray(Barray &&in)
: a(in.a)
, size(in.size) {
in.a = nullptr;
}
This can save a lot of copying!